The invention relates generally to data signal generation and, more particularly, the invention relates to a circuit for conditioning data signals.
Testing equipment has been used for many years to evaluate the performance of integrated circuits prior to their shipment to customers. Among other things, testing equipment typically includes a large number of xe2x80x9cpin cardsxe2x80x9d that each have circuitry for communicating with one corresponding pin of the integrated circuit being tested (referred to in the art as the xe2x80x9cdevice under test,xe2x80x9d or xe2x80x9cDUTxe2x80x9d). Each pin card may include a so-called xe2x80x9cpin driverxe2x80x9d for transmitting a test signal to its corresponding pin on the DUT. To that end, the pin driver typically is connected to its corresponding pin via a relatively short transmission line. For additional background information relating to testing equipment and pin drivers, see U.S. Pat. No. 5,010,297, the disclosure of which is incorporated herein, in its entirety, by reference.
The pin driver may transmit many different types of test signals to the DUT. One such test signal may be a pulse with a very short rise time. As known by those skilled in the art, pulses with short rise times have associated high frequency components that are filtered out when transmitted through a transmission line. For example, it is very likely that the high frequency components of one such pulse would be filtered out when transmitted through a transmission line typically used with the above discussed testing equipment. Consequently, if transmitted through the noted transmission line, such pulse undesirably would be received by the DUT with a much longer rise time. Moreover, the rise time may be substantially nonlinear. In other words, the test signal received by the DUT often is a significantly distorted version of that transmitted. To ensure the accuracy of the test, however, a precise pulse similar to that transmitted by the pin driver should be received by the DUT.
In accordance with one aspect of the invention, an apparatus for conditioning an output waveform delivered from a testing device produces an output voltage that is the sum of a control voltage and an input voltage. To that end, the apparatus includes an input for receiving the input voltage, and an output capable of producing the output voltage. The output is coupled with the testing device. The apparatus further includes a voltage element coupled between the input and the output, and a switching element to alternatively charge and discharge the voltage element. The switching element controls the voltage element to change the control voltage between a first voltage and a second voltage. Consequently, the output voltage is the sum of the control voltage and the input voltage.
In illustrative embodiments, the output waveform is clamped by the sum of the control voltage and the input voltage. The voltage element may include a resistance and a capacitance. For example, the voltage element may include a resistor in parallel with a capacitor. In such case, the control voltage has an associated decay rate that is a function of the resistance and capacitance of the voltage element.
In other embodiments, the control voltage is produced by a current transmitting through a resistance, and the current is controllable to control the amplitude of the control voltage. The switching element may include a first switch along a first current path, and a second switch along a second current path. The first current path is in parallel with the second current path. The control voltage may be either one of a positive or negative voltage.
In accordance with another aspect of the invention, a circuit for controlling the output voltage produced by a Class-AB driver includes an input for receiving an input DC voltage, and an output coupled with the Class-AB driver. The output has an associated output voltage. In addition, the circuit also has a voltage element coupled between the input and the output, and a switching element to alternatively charge and discharge the voltage element. The voltage element is controlled by the switching element to have a control voltage between a first voltage and a second voltage. The output voltage is the sum of the control voltage and the input voltage.
In some embodiments, the output waveform is clamped by the output voltage of the circuit. Moreover, the voltage element may include a resistance and a capacitance. In such case, the control voltage has an associated decay rate that is a function of the resistance and capacitance of the voltage element. The control voltage may be one of a positive voltage and a negative voltage.